Liz Buchanan BVSc MRCVS
It is quite easy for your vets to test the urine to make sure that it is too concentrated and not, for instance, excessive red blood cells being broken down so changing the colour of the urine (jaundice), or crystals, prostatitis or bladder stones etc. Urine associated with diabetes can sometimes look very yellow, with you mentioming ample water intake; usually the water intake of undiagnosed diabetics is excessive. Urine concentration can also provide an indication of kidney health. Your vet would need a fresh urine sample to start tests off for most of these things, so never underestimate the value of catching one in a clean (and dry!) tub on your way to the vets. They might even run one before an appointnent, if it might be urgent for example. I have heard of people adding salt to drinking water or diet but we would strongly advise againt this because besides tasting disgusting, dogs with a high salt intake simply need more water to compensate for it and often get sick, so it doesn't really solve anything. I hope that something there helps!